1. Field of the Invention
The present invention relates to a display unit having a complete solid sealing structure wherein a driving substrate provided with a display area and a sealing substrate are bonded with an adhesive layer in between and its manufacturing method, and more particularly such a display unit wherein organic light emitting device is provided in its display area and its manufacturing method.
2. Description of the Related Art
As a display unit instead of a liquid crystal display, an organic light emitting display which uses organic light emitting device has been noted. The organic light emitting display has characteristics that its visual field angle is wide and its power consumption is low since it is a self-light emitting type display. The organic light emitting display is also thought of as a display having sufficient response to high-definition high-speed video signals, and is under development toward the practical use.
There is the possibility that in the organic light emitting display, an area which emits no light (dark spot) is generated and luminance deteriorates due to intrusion of moisture, oxygen and the like into the organic light emitting device. Thus, a sealing technique to inhibit intrusion of moisture or oxygen is essential. Conventionally, a measure has been taken in such a way that an adhesive is applied to a rim part of a rear panel, a sealing can made of metal or glass is bonded thereto, and a getter material such as calcium is enclosed in the space between the rear panel and the sealing can. This sealing method by using such sealing can, however, has problems in its manufacturing process and its cost. In addition, there is the possibility that intrusion of the moisture through the adhesive or the like into inside of the sealing can cannot be completely prevented.
In order to block moisture or oxygen, a structure wherein the organic light emitting device or the sealing can is covered with a thin film whose main components are a seal material and carbon has been suggested. (For example, refer to Japanese Unexamined Patent Application Publication Nos. 2002-93586 and 2002-93576.) However, in the case where sealing is made by covering the organic light emitting device by the thin film, there is a problem that a part which is not covered with the thin film is generated due to exfoliation of the thin film caused by residual stress and low step coverage. Therefore, in this case, it is difficult to completely block moisture, oxygen and the like from intruding into the organic light emitting device.
Consequently, a complete solid sealing structure wherein a driving substrate provided with organic light emitting device and a sealing substrate are bonded with an adhesive layer in between has been developed. In such complete solid sealing structure, there is no remaining clearance between the organic light emitting device and the sealing substrate, which causes intrusion of moisture or oxygen, so that reliability of a display can be improved.
In some complete solid sealing structures, the organic light emitting device formed on the driving substrate are covered with a protective film (passivation film). A peripheral frame area of the driving substrate is an external connection area provided with an external connection terminal to make connection between the organic light emitting device and a drive circuit or the like. When the protective film is formed on this external connection terminal, reliability of the terminal might be lowered. Therefore, conventionally, when the protective film is formed, the external connection terminal was masked. However, since masking causes limitation of active agent and separation of plasma, a film thickness distribution of the protective film at mask edge matters in general deposition processes such as sputter deposition, CVD (chemical vapor deposition) and the like, particularly in CVD. Namely, a film thickness of the protective film increases with a slant, and in the CVD process, though depending on a mask thickness and a shape, a width of about 5 mm may be necessary to obtain 90% of a given film thickness. Therefore, the frame area, i.e. the external connection area tends to be larger. In addition, there is the possibility that a distance between the slanting end face of the protective film and the organic light emitting device becomes short, leading to easy intrusion of moisture and the like, and then causing lowering of reliability of the organic light emitting device.
The above problems can be dealt by making the mask thickness thin. However, making the mask thickness thin causes lowering of adhesion of the mask. In particular, in some cases of the CVD process which has wraparound, the protective film gets into the clearance between the mask and a substrate or the external connection terminal, and reliability of the external connection terminal is ruined.